They don't have new sets every month. They vary on previous sets. Well duh to your second point. It is cheaper to bring around 1 set than 2. Less sets = less trucks needed = less petrol for trucks = less truck drivers for them to pay = less road tax for trucks = less insurance for their drivers = less money for toll booths.

All of these have had large price increases, especially fuel. It all adds up.

They don't have to completely change the HD screen or what not, but geez it wouldn't hurt to add a few things to make Smackdown seem more like a different show. They could even add a carpet to the ramp if anything. The days of the Smackdown fist are definitely gone.